11 files changed, 124 insertions, 27 deletions

diff --git a/src/model/density_legend_geometry.c b/src/model/density_legend_geometry.c
new file mode 100644
index 0000000..ab3e46c
--- a/dev/null
+++ b/src/model/density_legend_geometry.c
@@ -0,0 +1,81 @@
+#include "density_legend_geometry.h"
+#include "../view/exp004state0.h"
+#include "../controller/exp004reshape.h"
+#include <GL/glut.h>
+#include <stdio.h>
+
+#define S exp004state0
+
+void
+density_legend_geometry (void)
+{
+  glNewList (S.list_offset + DENSITY_LEGEND_GEOMETRY, GL_COMPILE);
+  glPolygonMode (GL_FRONT, GL_FILL);
+  glColor4f (DEFAULT_COLOR_R, DEFAULT_COLOR_G, DEFAULT_COLOR_B,
+             DEFAULT_COLOR_A);
+
+  /*
+   * This value should be a percentage of the world height so that it
+   * remains a fixed number of pixels tall when the window is resized
+   * or zoomed.
+   */
+  double legend_height = 0.5;
+
+  /*
+   * Calculate the bounding box for the legend.
+   */
+
+  double a[2];
+  double b[2];
+  double c[2];
+  double d[2];
+
+  const double *left;
+  const double *right;
+  const double *top;
+
+  if (S.zoom.active)
+    {
+      left = &S.zoom.coords[0];
+      right = &S.zoom.coords[1];
+      top = &S.zoom.coords[3];
+    }
+  else
+    {
+      left = &S.ortho.min_x;
+      top = &S.ortho.max_y;
+      right = &S.ortho.max_x;
+    }
+
+  a[0] = *left;
+  a[1] = *top;
+  b[0] = *right;
+  b[1] = *top;
+  c[0] = *right;
+  c[1] = *top - legend_height;
+  d[0] = *left;
+  d[1] = *top - legend_height;
+
+  /*
+   * Overlay a legend from default saturation / alpha to full saturation.
+   */
+  for (int i = 1; i <= 1 / DEFAULT_COLOR_A; i++)
+    {
+      glBegin (GL_QUADS);
+      glVertex2dv (a);
+      glVertex2dv (b);
+      glVertex2dv (c);
+      glVertex2dv (d);
+      glEnd ();
+
+      /*
+       * Step left to right along the x-coordinate.
+       */
+      a[0] = *left + (*right - *left) * (DEFAULT_COLOR_A * i);
+      d[0] = a[0];
+    }
+
+  glEndList ();
+
+  return;
+}